Treatment of various medical conditions commonly involves implantation of medical devices and prostheses into a body. Examples of implantable devices for treatment include a stent device or graft placed into a diseased vein or artery, a catheter, and a fistula. Other devices are partially or temporarily placed in a body or positioned external to a body. Implantable medical devices are commonly used in various medical applications including cardiovascular, urological, gastrointestinal, and gynecological applications.
Various implantable medical devices can be deployed within the lumen of a body vessel using minimally-invasive transcatheter techniques. For example, implantable medical devices can function as a stent, a shunt, or a replacement valve. Such devices can include an expandable frame configured for implantation in the lumen of a body vessel, such as an artery or a vein. Minimally-invasive techniques and instruments for placement of endoluminal and intralumenal medical devices have been developed to treat and repair undesirable conditions by implantation of a medical device at a body vessel.
The use of stent-graft medical devices, or other types of endoluminal mechanical support devices has developed into a primary therapy for lumen stenosis or obstruction. Stents in body lumens are commonly used to maintain open passageways such as the prostatic urethra, the esophagus, the biliary tract, intestines, and various coronary arteries and veins, as well as more remote cardiovascular vessels such as the femoral artery, etc. Stents and grafts may be designed for either temporary placement—to maintain the patency of the body lumen—or permanent placement. Grafts and similar devices are also commonly configured as artificial conduits.
A common problem with implantable vascular prostheses is intimal hyperplasia after intervention in the vessel, such as a coronary artery. For example, a significant percentage of arterial bypass grafts and vein grafts fail due to intimal hyperplasia after coronary bypass surgery. Endothelial denudation, platelet adherence, and leukocyte infiltration are some of the functions which can contribute to the proliferation of vascular smooth muscle cells (VSMCs) in the vessel and subsequent onset of arterial stenosis.
There is a need for an effective, biocompatible approach for securing an implantable medical device into or onto biological tissue within a body vessel. Existing approaches to securing implantable medical devices have had limited success. In one approach, the medical device is anchored to the surrounding tissues by physical or mechanical means. Another approach is directed to modifying the medical device surface or material to induce the production of fibrous (scar) tissue to anchor the medical device upon implantation within the body vessel.
There is a need to reduce or prevent the formation of biofilm and infection from bacteria and other microorganisms on catheters, orthopedic implants, pacemakers, contact lenses, stents, vascular grafts, embolic devices, aneurysm repair devices and other medical devices. There is also a need in the art for materials and structures that can replace or improve biological functions or promote the growth of new tissue in a subject. Tissue regeneration may be influenced by porosity among other factors.
Conventional grafts are made from various biocompatible plastics and metals such as poly(ethylene terephthalate) (PET). Such stents are known to cause irritation and undesirable biologic responses from the surrounding tissues in a lumen. Although conventional permanent medical devices are designed to be implanted for an extended period of time, it is sometimes necessary to remove the device prematurely, for example, because of poor patency or harsh biological responses. In this case, the device generally must be removed through a secondary surgical procedure. The surgical removal of the device will resultingly cause undesirable pain and discomfort to the patient and possibly additional trauma to the lumen tissue. In addition to the pain and discomfort, the patient must be subjected to an additional time consuming and complicated surgical procedure with the attendant risks of surgery.
Polyurethane (PU) and PU-based devices have commonly used for vascular grafts, blood conduits, and other devices for several decades. More recently, the use of PU for medical devices has been called into question. For example, PU-based vascular grafts have excellent records in animal trials but disappointing results in clinical applications. PU-based grafts have problematic long-term in vivo biostability and raise carcinogenic concerns as they degrade in the body. Thus, there is a need for implantable medical devices with biocompatibility, which is influenced by surface chemistry and topography.
Bioabsorbable and biodegradable materials have emerged more recently as a common material for medical devices. The conventional bioabsorbable or bioresorbable materials from which such stents and grafts are made are selected to absorb or degrade over time, thereby eliminating the need for subsequent surgical procedures to remove the stent from the body lumen. Such bioabsorbable and biodegradable materials also tend to have superior biocompatibility characteristics to biocompatible metals and other materials.
There are, however, known disadvantages associated with the use of bioabsorbable or biodegradable materials. One of the problems is that the materials break down at a faster rate than is desirable for the application. Premature degradation can lessen the affectivity of the device. Another problem is that conventional materials may break down into large, rigid fragments which may cause obstructions in the interior of a lumen, such as the urethra. Alternatively, the materials may take too long to breakdown and stay in the target lumen for a considerable period of time after their therapeutic use has been accomplished.
There is also the need to provide medical devices having mechanical compatibility or enhanced mechanical properties. For example, a mismatch between the stiffness, hardness, and porosity of the device in comparison to the surround tissue environment can cause irritation and other complications after implantation. In more drastic cases, the device can damage the tissue wall. There is also a need for devices have enhanced mechanical properties such as increased wall strength. Such properties may be useful for enabling easier navigation through the body and increased patency.
There is a need for medical devices and prostheses, and in particular implantable medical devices, which overcome these and other problems.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.